As part of the World Health Organization (WHO), the International Agency for Research on Cancer (IARC) works to identify potential carcinogenic hazards to humans. Its decisions influence public health policies worldwide, making transparency and objectivity in its processes essential. However, concerns have been raised about conflicts of interest (COIs) within IARC’s decision-making framework, particularly regarding the selection of working group members and the data reviewed.

Senior Pathologist Tracey Papenfuss, DVM, MS, PhD, DACVP, co-authored a 2025 article that aims to raise awareness of and address these conflicts of interest (COIs). The review, published in the Human and Experimental Biology and titled, “Conflicts of interest in the International Agency for Research on Cancer process of identifying carcinogenic hazards to humans,” focused on the identification and management of conflicts of interest in scientific decision making as it pertains to identifying carcinogenic hazard assessment. The full article was published in the June 2025 edition of Human & Experimental Toxicology.

Hazard identification vs. risk assessment

IARC focuses on hazard identification, which examines whether a substance has the potential to cause harm under any circumstances. This differs from risk assessment, which evaluates the likelihood of harm under real-world conditions. While both processes are important, they rely on different methodologies and data sets, leading to potential discrepancies in conclusions.

Conflicts of interest in IARC working groups

Managing COIs is crucial for ensuring unbiased scientific decision-making. IARC requires working group members to complete a Declaration of Interests (DOI) form, disclosing financial and non-financial interests. However, the agency does not consider prior professional experience with the substance under review as a COI. This policy has sparked criticism, as such experience can lead to pre-existing biases that may compromise objectivity.

Recommendations for reducing bias

Dr. Papenfuss and her co-authors included many proposals for measures to minimize bias in IARC’s processes:

1. Reclassify experts with COIs as Invited Specialists: Scientists with substantial professional experience related to a substance should serve as non-voting Invited Specialists rather than voting members. This would allow them to contribute their expertise without influencing final decisions.
2. Expand data inclusion criteria: IARC currently limits its reviews to select published studies, excluding unpublished data and high-quality review articles. To ensure comprehensive assessments, the agency should include all relevant toxicological studies, including those relied upon by regulatory agencies in WHO member countries.
3. Independent panel for data selection: An independent panel of experts should determine which studies are shared with working groups. This would reduce the risk of bias stemming from the IARC Secretariat’s selective screening process.
4. Reinstate “Probably Not Carcinogenic to Humans” classification: Since 2019, IARC has removed the option to classify substances as “probably not carcinogenic to humans.” Reinstating this category would provide a more balanced framework for hazard identification.
5. Increase transparency: Meeting minutes, including vote totals and summaries of divergent opinions, should be publicly available. Additionally, participants’ curricula vitae and COI declarations should be accessible to the global scientific community and the public.

The role of professional experience

While expertise is essential for evaluating complex scientific data, prior professional experience with a substance can introduce bias.  Scientists may be motivated to validate their previous findings or secure future funding, consulting opportunities, or professional accolades. This dynamic underscores the need for stricter COI policies within IARC.

The review draws an analogy to juries, which are expected to render impartial verdicts based on evidence presented in court. Just as potential jurors with pre-formed opinions are excluded, IARC working group members should evaluate evidence without the influence of prior biases.

Improving IARC’s credibility

This paper emphasizes that IARC’s decisions have far-reaching implications for public health and environmental policies. Enhancing transparency and objectivity in its processes would strengthen public trust and scientific integrity.  Collaboration among regulators, scientists, industry representatives, and public health advocates can further refine IARC’s approach to hazard characterization.

Reaffirming scientific integrity and accountability in the IARC’s decision-making processes

While IARC’s mission to protect public health is commendable, its processes for identifying carcinogenic hazards require updates to minimize bias and COIs. By implementing the recommendations proposed by the authors of this paper, the IARC can enhance the credibility and impact of its assessments. Open dialogue and constructive feedback from stakeholders will be essential in achieving these goals.

By addressing COIs, expanding data inclusion criteria, and increasing transparency, IARC can ensure that its hazard assessments are both rigorous and impartial, ultimately benefiting global public health.

Access the full review published in Human & Experimental Toxicology

Download the review article here.